1. Field of the Invention
The present invention relates to an etching method and particularly to an etching method which can reduce a microloading effect.
2. Description of the Prior Art
Electronic devices, such as integrated circuits, are formed by deposition, growth and etching of material on a substrate. In a typical etching process, a patterned mask is formed on the substrate by a conventional photolithographic process, and then exposed portions of the substrate are etched away. In the etching process, it is desirable to control the dimensions of the features being etched. Conventional etching processes, however, often result in non-uniform etching rates and microloading effects across the substrate.
The mask layer such as a photoresist is formed by a spin coating process on the substrate or a material layer which is going to be etched. The thickness of the mask layer is influenced by the density of the material layer underneath the mask layer. The spin coating process spreads the mask layer uniformly. Therefore, the mask layer distributes the same volume within a high density region of the material layer and a low density region of the material layer. Because the high density region has a greater density of the material layer, the mask layer is heightened. As a result, the top surface of the mask layer within the high density region is higher than the top surface of the mask layer within the low density region. Different heights of the top surfaces of the mask layer will cause differences in thickness of the material layer within the high density region and the low density region after an etching process.